Fluid control valve and braking system incorporating such a valve

ABSTRACT

A fluid flow valve having a body ( 11 ) with first, second and third fluid inlets ( 8, 18, 25 ), a working fluid outlet ( 4 ), a first pressure element ( 11 ) movable, under the influence of pilot pressure fluid applied to the first inlet, from a first position in which it causes closure of the second inlet, to a second position in which it causes opening of the second inlet, and a second pressure element ( 20 ) movable, in response to pressure at the fluid outlet, from a first position in which it causes closure of the third inlet ( 25 ) to a second position in which it causes opening of the third inlet, said elements ( 11, 20 ) operating in conjunction to permit an initial high volume fluid flow from the second inlet through the outlet and subsequently, with the second element causing interruption of a path between the second inlet and outlet, a high pressure fluid flow from the third inlet through the outlet. The invention embraces a vehicle braking system incorporating the aforesaid valve.

This invention relates to a fluid control valve, primarily for use in avehicle braking system, and operable, in use, to permit the applicationto a brake of a relatively large volume of fluid for the take-up ofbrake clearances and/or brake cooling, as well as to permit actuation ofthe brake by the supply thereto of high pressure fluid. The inventionalso embraces a braking system incorporating such a valve.

In some conventional braking systems, particularly for commercial oragricultural use, large slave cylinders are employed having a verysignificant fluid capacity, requiring, in turn, the use ofcorrespondingly large master cylinders. Such arrangements can bedisadvantageous, in terms both of the considerable space required tohouse them on a vehicle and also because operation of the mastercylinders can require large pedal efforts or travel.

An object of the invention is to alleviate the aforesaid problems byproviding a fluid control valve for use in a vehicle braking systemwhich controls the flow of low pressure fluid to a brake from a fluidsource independent of the master cylinder. A further object is toprovide a braking system incorporating such a valve.

According to a first aspect of the invention, a fluid flow valvecomprises a body having first, second and third fluid inlets, a workingfluid outlet, a first pressure element movable, under the influence ofpilot pressure fluid applied to the first inlet, from a first positionin which it causes closure of the second inlet, to a second position inwhich it causes opening of the second inlet, and a second pressureelement movable, in response to pressure at the fluid outlet, from afirst position in which it causes closure of the third inlet to a secondposition in which it causes opening of the third inlet, said elementsoperating in conjunction to permit an initial high volume fluid flowfrom the second inlet through the outlet and subsequently, with thesecond element causing interruption of a path between the second inletand outlet, a high pressure fluid flow from the third inlet through theoutlet.

In one convenient arrangement, a further outlet of the body forconnection to an external low pressure region is connected within thebody to the working outlet when the first pressure element is in itsfirst position and prevented from communicating with the working outletby the first pressure element when in its second position.

Preferably, the pressure elements are pistons slidable within the bodyand, conveniently, telescoped one within the other.

From another aspect of the invention, a vehicle braking system comprisesa fluid control valve in accordance with the aforesaid first aspect ofthe invention, a source of pilot pressure fluid connected to the firstinlet, a fluid source capable of providing a relatively high volumesupply of fluid connected to the second inlet, a high pressure fluidsource connected to the third inlet and a brake connected to the workingfluid outlet, the arrangement being such that pilot pressure applied viathe first inlet to the first pressure element causes movement of thelatter to open the second inlet for admission of a high volume fluidflow through the working fluid outlet, the second fluid pressure elementbeing exposed to and moved by the pressure of the high volume fluidacting thereon to close the second inlet and open the third inletthrough which high pressure fluid is then admitted to the brake via theworking fluid outlet for brake actuation.

Conveniently, a hydrostatic master cylinder may be the source of boththe pilot pressure and high pressure fluid, the high volume fluid beingtypically provided from a hydrodynamic fluid source.

Alternatively, a hydrodynamic fluid supply may be used, conveniently viaa power valve, to provide both the high volume fluid and high pressurefluid. It would also be possible to derive the pilot pressure from thehydrodynamic supply via the power valve.

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a longitudinal cross-section of one form of the fluid controlvalve of the invention in a non-operative or passive condition;

FIG. 2 is a view similar to FIG. 1 of the valve in another operativeposition;

FIG. 3 is a view similar to FIGS. 1 and 2 of the valve in a furtheroperative position;

FIG. 4 illustrates the valve of FIG. 1 incorporated in a braking systemwhich is depicted schematically;

FIG. 5 illustrates the valve of FIG. 1 incorporated into an alternativebraking system depicted schematically;

FIG. 6 illustrates the valve of FIG. 1 incorporated in a furtheralternative braking system, depicted schematically;

FIG. 7 illustrates the valve of FIG. 1 incorporated into a furtheralternative braking system depicted schematically, and

FIG. 8 illustrates the valve of the invention in a form permitting thesupply of cooling fluid to a brake.

The fluid control valve illustrated in FIG. 1 has a body 1 formed with aco-axial stepped bore providing a larger diameter bore portion 2 and asmaller diameter bore portion 3. The bore portion 3 is blind,communicating with the exterior by way of a port 4 provided in theclosed end 5 of the body. The bore portion 2 has an open end closed by acap 6 secured to the body by fastening means illustrated as bolts 7. Thecap contains a pilot pressure inlet port 8 and a bleed port 9communicating with a bleed passage 10 through the cap.

The larger diameter bore portion 2 contains a hollow piston 11 which isurged by a spring 12 towards a leftward position in which a solid end 13thereof abuts against the end cap 6. The end 13 is peripherally groovedto receive a pressure seal 14. The outer surface of the piston 11 isrelieved to provide an annular recess 11A delimiting a pair of axiallyspaced lands 15, 16, which are disposed respectively adjacent a fluidreturn to tank port 17 and an hydraulic inlet 18. The land 16 isprovided with a seal arrangement 19. A further piston 20 is slidablymounted within the hollow piston 11 and urged by a spring 21 towards aposition in which it engages the solid end 5 of the body. The piston 20is provided along a major part of its length with an axial passage 22which forms a connection between a diametral passage 23 and the fluidoutlet 4. The passage 23 is arranged to be adjacent a pair ofdiametrically opposed radial passages 13A, 13B through the wall of thepiston 11. The piston 20 is provided with a pair of axially spaced seals20A, 20B.

The principal operational function of the valve described above is toeffect the filling of one or more large volume brake slave cylinderswith low pressure hydraulic oil from a hydrodynamic hydraulic supplycircuit of a vehicle, prior to the application to the cylinders of fluidunder high pressure to create the necessary braking force. In use, thepilot pressure inlet port 8 is connected to a source of hydraulicpressure, which may conveniently be derived from a master cylinder ofthe braking system, as will be described hereafter. The hydraulic oilpressure inlet port 18 is connected to a source of hydrodynamic fluidpressure derived conveniently from an auxiliary hydraulic pump of thevehicle. The body 1 is provided with a high pressure brake fluid inlet25 connected, in use, to a conventional pressure device such as adriver-operated master cylinder.

A braking operation is initiated by the application of a pilot pressurevia the inlet 8 to the adjacent end area of the piston 11, causing it tomove through a distance ‘l ’ relative to the piston 20 to the positionshown in FIG. 2, in which it abuts the opposing end face of the solidend 5 of the body. During this movement, the spring 12 is compressed andthereby stores a return force. The space 2 beyond the forward end of thepiston 11 remote from the pilot pressure inlet 8 is permanentlyconnected by a passage 1 7A to the tank port 17 to prevent a build-up ofpressure in the space 2 upon movement of the piston. The aforesaidmovement of the piston 11 through distance ‘l ’ brings the land 15 to aposition in which it blocks the fluid return to tank port 17 and alsomoves the land 16 and its seal to at least partially uncover thehydraulic oil pressure inlet port 18, permitting oil therefrom to flowinto the adjacent recess 11A in the piston 11, through the radialpassage 13A of the piston 11 and thence through the diametral passage 23and axial passage 22 of the piston 20 to the outlet 4 leading to thebrake. This enables a large volume of relatively low pressure fluid fromthe hydrodynamic fluid source to be transmitted into the brake in orderto take up brake clearances therein, prior to the brake beingpressurized from the master cylinder for brake actuation. Once the brakeclearances are taken up, the relatively low pressure feeding back ontothe adjacent end face of the piston 20 creates sufficient force to movethis piston to the left against the action of the spring 21 to theposition shown in FIG. 3. Such leftward movement of the piston 20 takesplace through a distance sufficient for the seal 20B to clear thehydraulic brake pressure inlet 25, simultaneously moving the seal 20Ainto a position to block the radial passages 13A, 13B, so as to cut offthe supply of hydraulic oil from the inlet 18 to the passage 22.Leftward movement of the piston 20 also compresses a stack of Bellevillewashers 30 against the adjacent inner surface of the end 13 of thepiston 11, such compression contributing to a progressive pedal feelexperienced by the driver.

When braking pressure is released from the inlet 25 and the pilotpressure from the inlet 8, the pressure at the outlet 4 decays, enablingthe spring 21 to return the piston 20 towards its initial position (FIG.1), thereby reconnecting the passage 22 via the passages 23, 13A, 13B tothe return outlet 17, permitting fluid to be discharged, as required,upon release of the brake.

FIG. 4 illustrates schematically a braking system incorporating thevalve of FIGS. 1 to 3. The system includes a master cylinder 40 operableby a brake pedal 41, the master cylinder being connected by a line 42 toa remote booster 43 via which is operated a brake actuating mastercylinder 44. A branch line 48 from the line 42 is connected to the pilotpressure inlet 8 of the valve. The booster 43 is actuated by ahydrodynamic fluid supply via line 45, from which a branch 46 isconnected to the low pressure fluid inlet 18. The output from the mastercylinder 44 is supplied via line 47 to the brake pressure fluid inlet25. Initial pressure on the brake pedal 41 causes a pilot pressure to beapplied at the inlet 8, which moves the piston 11 of the valve to theposition illustrated in FIG. 2 allowing the brake to be rapidly filled,via the inlet 18, with a large volume of fluid for brake clearancetake-up. This action is followed by leftward movement of the piston 20,as previously described, to close off the inlet 18 and open inlet 25,permitting high pressure fluid to be supplied from the master cylinder44 along line 47 into inlet 25 for brake actuation. Release of the brakepedal and consequent decay of braking pressure permits the pistons tore-assume their illustrated rest positions.

In the system illustrated in FIG. 5, a tandem master cylinder 50 isused, enabling a pilot pressure to be generated in one part of themaster cylinder and transmitted via a line 51 to the pilot pressureinlet 8. The brake actuating pressure is generated in the other part ofthe master cylinder and transmitted via a line 52 to the brake pressureinlet 25. The low pressure high volume fluid is applied to the inlet 18from an auxiliary pumped hydrodynamic supply of the vehicle, as before.Operation of the valve is identical to that described previously.

In the system described in FIG. 6, a single master cylinder 60 is usedto provide both the pilot pressure and brake actuating pressure. Themaster cylinder output is connected via line 61 to the pilot pressureinlet 8 and via line 62 to the actuating pressure inlet 25. As in. theprevious embodiment, the high volume supply is provided at inlet 18 froma pumped auxiliary system of the vehicle. Actuation of the brake pedalwill cause the valve initially to supply the brake rapidly with lowpressure fluid and subsequently with fluid at brake actuating pressure,as described above.

A further alternative system of the invention is illustrated in FIG. 7and employs a power valve 70 actuated by a driver-operated pedal 71. Thepower valve receives oil from a hydrodynamic source, such as apump-operated system of a vehicle, through line 72, from which a branch73 applies the fluid to the inlet 18. Fluid leaving the valve 70 isdirected along a branch 74 to the pilot inlet 8 and along a branch 75 tothe actuating pressure inlet 25. In this case, it will be seen that thepilot pressure and brake actuating pressure are both taken from thepower valve 70. Operation of the valve is as described previously.

The valve illustrated in FIG. 8 is generally similar to that of FIGS. 1to 7, but modified to enable a supply of cooling fluid to be applied toa brake, in addition to providing the other functions described above.The major components of the valve are the same as those describedpreviously, notably comprising the body 1 closed by an end cap 6 andcontaining the larger and smaller diameter mutually telescoped pistons11 and 20, the body having inlets 8, 18 and 25 and outlets 4 and 17arranged generally as previously described. The body now has anadditional outlet 80 for cooling fluid opening into the body at theleft-hand side of the land 15 and the piston 11 has axially spaced pairs81, 82 of aligned through radial passages in its cylindrical wall, thepassages of each pair being arranged respectively at either side of theland 15. The small diameter piston 20 is provided with a further radialpassage 83 in addition to the existing passage 23, the passage 83communicating via an axial hole 83A with a chamber 83B containing theBelleville washers 30. Additional seals 84 are provided respectively ateither side of the passage 83.

In operation, pilot pressure applied to the inlet 18 causes successivemovement of the pistons 11 and 20 to effect brake filling and pressurebraking operations, as described previously. At this stage, the inletport 18 is uncovered, allowing low pressure oil into the annular recess11A between the lands 15, 16. As the inner piston moves away from theoutlet 4, the left hand one of the additional seals 84 moves to theopposite side of the passage 82, establishing communication between theinlet port 18 and outlet port 80 via passages 82, 83, hole 83A, chamber83B and passages 81. A relatively large volume of low pressure fluid isthus supplied to the brake via outlet port 80 during brake actuation andcan serve, for example, for brake cooling. Removal of the pilot pressurefrom the inlet 18 causes the valve to return to the illustrated initialposition.

It will be understood that the valve may be arranged differently fromthat in the embodiments described. For example, it is not necessary forthe pistons to be telescoped one within the other, although this isdesirable for space-saving and simplicity. It is possible for at leastthe pilot pressure input to be pneumatic rather than hydraulic.

The foregoing description is exemplary rather than defined by thelimitations within. Many modifications and variations of the presentinvention are possible in light of the above teachings. The preferredembodiments of this invention have been disclosed, however, one ofordinary skill in the art would recognize that certain modificationswould come within the scope of this invention. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described. For thatreason the following claims should be studied to determine the truescope and content of this invention.

What is claimed is:
 1. A fluid flow valve comprising a body havingfirst, second and third fluid inlets, a working fluid outlet, a firstpressure element movable, under the influence of pilot pressure fluidapplied to the first inlet, from a first position in which it causesclosure of the second inlet, to a second position in which it causesopening of the second inlet, and a second pressure element movable, inresponse to pressure at the fluid outlet, from a first position in whichit causes closure of the third inlet to a second position in which itcauses opening of the third inlet, said elements operating inconjunction to permit an initial high volume fluid flow from the secondinlet through the outlet and subsequently, with the second elementcausing interruption of a path between the second inlet and outlet, ahigh pressure fluid flow from the third inlet through the outlet.
 2. Avalve according to claim 1, wherein a further outlet of the body forconnection to an external low pressure region is connected within thebody to the working outlet when the first pressure element is in itsrespective first position and prevented from communicating with theworking outlet by the first pressure element when in its secondposition.
 3. A valve according to claim 1, wherein the pressure elementsare pistons slidable within the body.
 4. A valve according to claim 3,wherein the pistons are telescoped one within the other.
 5. A valveaccording to claim 1, wherein the first and second elements arespring-urged in opposite directions towards abutment against respectiveoppositely facing surfaces of the body.
 6. A valve according to claim 1,wherein the first pressure element in its second position opens a pathextending through both pressure elements between the second inlet andthe outlet, and the second pressure element in its second position opensa direct path between the third inlet and the outlet, whilst closingsaid path between the second inlet and the outlet.
 7. A valve accordingto claim 1, wherein the first and second pressure elements cooperate toprovide a low pressure fluid flow from the body during high pressurebrake actuator flow through said outlet.
 8. A valve according to claim7, wherein movement of the second pressure element to its secondposition opens a passage in the first pressure element such as to placethe second inlet in communication with a port through which said lowpressure fluid flow takes place during high pressure brake actuatingflow through said outlet.
 9. A vehicle braking system comprising a fluidcontrol valve in accordance with any one of the preceding claims, asource of pilot pressure fluid connected to the first inlet, a fluidsource capable of providing a relatively high volume supply of fluidconnected to the second inlet, a high pressure fluid source connected tothe third inlet and a brake connected to the working fluid outlet, thearrangement being such that pilot pressure applied via the first inletto the first pressure element causes movement of the latter to open thesecond inlet for admission of a high volume fluid flow through theworking fluid outlet, the second fluid pressure element being exposed toand moved by the pressure of the high volume fluid acting thereon toclose the second inlet and open the third inlet through which highpressure fluid is then admitted to the brake via the working fluidoutlet for brake actuation.
 10. A system according to claim 9, wherein ahydrostatic master cylinder serves as the source of both the pilotpressure and high pressure fluid.
 11. A system according to claim 10,wherein the master cylinder is connected to a booster which operates abrake actuating master cylinder from which high pressure fluid isapplied to the third valve inlet.
 12. A system according to claim 10,wherein the high volume fluid flow is provided from a hydrodynamic fluidsource.
 13. A system according to claim 10, wherein the hydrostaticmaster cylinder is a tandem master cylinder, one cylinder part of whichgenerates the pilot pressure and the other cylinder part of whichgenerates the brake actuating pressure.
 14. A system according to claim9, wherein a power valve receives fluid from a hydrodynamic source whichalso serves as the source of the low pressure fluid, said power valveproviding both the pilot and brake actuating pressures.